Depends on whether a service has been provided and after the revelation about Mario Batali stealing tips from his waitstaff, I ask about where the tip jar money goes. I do not assume that it goes to the cook staff that we seldom see.
I also tip if something is exceptional like the donut place I go when I head to Austin to see the grandkids. They have the best donuts and are very conscientious about the cleanliness of their restaurant.
I have this friend that I will not go to a restaurant with and he's a former restaurant owner. He will low tip or no tip and then reprimand the person telling them how to do their job. I will reward really good service and attiude but I don't low tip if the service wasn't good, these people get next to nothing in hourly pay and are tip dependent.
I have another friend that did something I'd not thought about, he also owned a very successful restaurant. He always asks the owner/manager if the waitstaff splits tips and if they do, he asks him if he can tip his usual of 25% for the split but give more than that directly to the waiter. He said if it's a fine dining restaurant, if the minimum for split is met, he's never been told he couldn't do that and they arrange that.